Lockout/tagout is a process by which a piece of equipment is secured against accidental energization during repairs or maintenance. Lockout/tagout procedures are designed to ensure energy sources are maintained in a “zero mechanical state” before and during repair or maintenance work on a piece of equipment or machinery. When working on equipment or machinery that is designed to move or has moving parts, it is important to recognize and control all possible energy sources: electrical, pneumatic, hydraulic, mechanical, chemical, thermal and stationary energy sources.
The United States Occupational and Health Administration (OSHA) has provided regulations for The Control of Hazardous Energy (Lockout/Tagout). Title 29 Code of Federal Regulations (CFR) Part 1910.147, addresses the practices and procedures necessary to disable machinery or equipment, thereby preventing the release of hazardous energy while employees perform servicing and maintenance activities. The standard outlines measures for controlling hazardous energies—electrical, mechanical, hydraulic, pneumatic, chemical, thermal, and other energy sources.
The first step in lockout/tagout is to determine and write down the energy source for the specific equipment. Many pieces of equipment have more than one energy source. For example, hydraulic or pneumatic presses have two energy sources: the electricity that runs the hydraulic or pneumatic pump and the stored pressure within the system. Then, the magnitude of power of each energy source must be determined and documented. For example, for a pneumatically driven press powered by electricity, the voltage of the electricity and pounds per square inch (psi) rating of the pneumatic or hydraulic system would be written down.
Lock vs. Tag
There are three allowable options for lockout/tagout: a lock alone, a tag alone (if it is not possible to install a lock) or, preferably, a lock and tag together. Locks alone create a safe situation but offer no explanation for the lockout. Although tags alone are permitted because some machines cannot be locked out, this is OSHA's least favorite method because it offers less of a guarantee for safety. Locks and tags together provide a visual and written explanation for lockouts while offering fail-safe protection from error.
If a tag is used alone, it must be demonstrated in the program that the tag offers the same level of employee protection as a lock and tag together. Additional training when only a tag is used is required because tags don't offer the same physical restraint as locks and employees must understand this. Although switches still can be activated, it is a safety hazard and a violation of the regulations and company policy to activate switches. Tagout devices must warn against a hazardous condition with a warning such as:
“Do Not Start”
“Do Not Open” “Do Not Close”
“Do Not Energize”
“Do Not Operate”.
Locks
Although the installation of equipment-specific lockout devices is generally a simple matter, the cost can be prohibitive. Fortunately, OSHA doesn't require the purchase of specific lockout devices for each valve, switch or circuit; it requires only that the mechanism that controls the power to the machine be secured. If the power source can be secured with a chain or something as durable and difficult to defeat, it is acceptable to use such means.
Removing Lockout Devices
The simplest way to unlock and restart equipment once maintenance work is completed is to reverse the steps followed to shut down the equipment. This may not be possible with all machines, however.
The first thing that always should be done is to replace all guards and protective devices that were on the machine originally. Then, all unnecessary objects must be removed and all unessential personnel asked to leave the area. Next, all employees involved should remove their own locks. No employee should remove another person's lock. When an authorized employee who applied a lockout device to a piece of equipment or machinery is not available to remove the device, the employer may remove the device provided that procedures and training for such a removal have been developed, documented and incorporated in the employers' lockout/tagout program.
Hot Tap
The “hot tap” procedure is employed in repair, maintenance, and service activities, and involves the cutting and welding of equipment (pipelines, vessels or tanks) under pressure in order to install connections or appurtenances. It is commonly used to replace or add sections of pipeline without the interruption of service for air, gas, water, steam and petrochemical distribution systems. Special metal cutting and welding equipment and specific operating procedures are used to limit explosion hazards. The operation may be performed by in-house maintenance personnel or by outside contractors.
The use of “hot tap” procedures appears to avoid several safety risks, which would otherwise arise in servicing equipment, which is under pressure. First, process shutdowns and startups of equipment of this nature pose extreme hazards of explosions and fire due to the type of materials being handled, and the complexities of and potential interactions between materials being conveyed or otherwise available in the workplace. For example, during startup it is necessary to purge pipelines of air, water and/or inert gases before hydrocarbons are introduced. Malfunctions or operator errors during purging could easily create explosive mixtures in the equipment. In other instances, process shutdowns and startups can result in rapid condensation within the process equipment and may cause “water hammers,” which are sudden pressure changes that can shake, vibrate and stress equipment to the extent that the pipeline breaks or connection leaks develop. Finally, a third class of hazard avoided is one created by the much higher level of worker activity required during a complete process shutdown or start-up. This may result in more extensive worker exposure to the hazards of the shutdown or start-up procedure, and in greater potential for injury than would be involved in performance of “hot tap” type activities, in which fewer employees would be exposed.
OSHA believes that employees performing hot tap operations should have comparable protection to workers performing other servicing or maintenance of machines or equipment. OSHA also believes that these operations should be allowed to be conducted when certain limited conditions exist, such as when continuity of service is essential and system shut down is impractical. By specifying these limitations the employer would be prohibited from conducting these operations simply as an expedient. The need for continuity of service would be illustrated by the pipeline containing a petroleum product where stopping the flow of the product and draining the pipeline could introduce an additional danger to employees since the concentration of the gaseous product remaining in the pipe, when mixed with air, could fall within the explosive range of the product, thereby threatening an employee with serious injury if that employee would attempt to weld on the pipe. In this case, shut down may not be practical because shutting down the system may prove more hazardous than allowing the continued operation of the system while the hot tap operation is being conducted. Another example would be when a large storage tank with a hazardous substance is punctured or otherwise penetrated. There is obviously little or no time available to continue the service (store the substance) and shut down the system (drain the tank). In this case, the hot tap operation could be safely and properly conducted if a documented procedure and the required equipment are used so that they provide effective protection for employees.
Fluids (Compressed Gases, Air, Steam, Hydraulics, Petroleum)
1. Compressed gas pressure systems are included under Title 29 and are required to be locked out/tagged out if pressures could result in unexpected movement of the equipment or components.
2. Equipment using air or other compressed gas must be equipped with a main line shut off valve capable of being locked out or tagged out in the “off” position.
3. Unless the compressed gas valve allows pressure release, a portion of the pipe shall be disconnected to allow pressure release if the trapped energy could create a possible hazard.
4. All compressed gas lines will be labeled. If labels do not exist, the employee shall notify their immediate supervisor and labeling will be applied.
Hydraulic Energy
Equipment using hydraulic pressure shall be locked out by placing the hydraulic pump motor electrical disconnect switch in the “OFF” position and applying a lockout/tagout device to the disconnect. Bleed off residual pressure in the piping system.
Food and Beverage
Food and beverage production is one of the most difficult and demanding environments for workplace safety products and identification. Harsh wash down cycles, chemical sanitizers, and constantly wet environments present reliability challenges requiring consistent maintenance and repair. While it is intuitive that liquid products, would require piping to facilitate their movement through the production process, dry granular solids, including (but not limited to) grains such as rice, corn, wheat and the like may be processed for marketing through piping systems. Of course, those of skill in the art will appreciate that there are many such dry, granular solids that are chemicals and other non-foodstuffs.
Work on Existing Piping Systems
Hazardous energy exists in piping systems, at least, in the form of steam, liquids, chemicals and dry granular solids. Program procedures for lockout/tagout should be followed when breaking into a line where there is potential for exposure to hazardous energy.
Many accidents occur because of the failure to verify that all energy sources have been isolated. In some instances, piping being serviced may be back-fed or be tapped into by several lines leading to an unexpected release. Process pipe drawings and/or plant maintenance personnel must be consulted to identify all lines feeding the system being serviced. In practice, the identification of all lines feeding into the system may not be obvious. There are instances where there are more than one source supplying a line to be disconnected and have work performed. When these multiple sources have limited chances for LO/TO, current methods are not enough to ensure the safety of the worker and the integrity of the line.
On steam systems above 15 psig, double valve protection is required when the work involved may jeopardize the integrity of the piping that the isolation valve is attached to. When working on a main steam line between two isolation valves of verified reliability, it is not necessary to close a second main steam valve upstream of the repair area. When working on a small diameter steam line such as a trap station line, the small diameter valve is not adequate isolation. The steam main valve on each side of the repair area must be closed. This distinction is necessary because of the possibility of breaking a smaller diameter valve and compromising the safety isolation.
On piping systems, the current method for lockout requires identifying the valves that control flow to the part of the system undergoing maintenance and locking out each one individually. The valves are then closed, and a cable is laced through the valve handle and tagged. Such valve-types include, but are not limited to, ball valves, butterfly valves, diaphragm valves, and gate valves. While with certain valve types, disabling a valve actuator may be as easy to accomplish as securing a cable through a hand wheel (such as with a gate valve), other valve types have only a handle (such as with a ball valve) or no handle at all, such as with a reversing valve. This makes lockout of such valve handles less easy.
Further, even in such situations, where a valve handle is easily secured, in many situations there are multiple valves leading to a piping section undergoing maintenance and repair. In such situations, there may be multiple valves in distant locales each under control of multiple individuals not personally undertaking the maintenance/repair. There are instances where there are more than one source supplying a line to be disconnected and have work performed. Therefore, the risk exists that either all the valves may not be shut off or that during maintenance someone may turn on a valve leading the maintenance section sending a fluid or gas to the repair site and causing injury to the repair crew.
Therefore, a need exists to provide a lockout system that does not require multiple lockout devices and is not remote from the supervision of the individual undertaking the repair at the locale where the maintenance is being performed.